1. Field of the Invention
The invention relates to gas turbines. More particularly, it relates to enhancing the output of gas turbines.
2. Description of the Prior Art
Moisture is often added to gaseous fuels entering combustors as a means of NO.sub.x control. For this purpose, water vapor addition to gas streams is generally accomplished through the direct addition of steam to a gas stream. For gas turbine combustors, fuel gas is commonly injected therein, at pressures in excess of 200 psia, with said moderate pressure steam providing the moisture needed for NO.sub.x control. The direct addition of steam to the fuel gas serves to provide mass to the fuel gas, which has a beneficial effect on the net power output from the gas turbine, in addition to providing the moisture needed for NO.sub.x control.
In many instances, the steam employed for NO.sub.x control can be more efficiently used in a steam turbine, producing more power than can be obtained by expanding the steam in a gas turbine. For example, 1000 pounds per hour at 250 psia saturated steam fed to a condensing turbine can produce 112 hp, while feeding the same amount of steam to an industrial gas will produce about 90 hp, because of the lower applicable pressure ratio, and require additional fuel to raise the temperature of the steam to that needed for optimum gas turbine operation.
In an alternative approach for adding moisture to a gas stream, a hot water steam is added to the fuel gas by means of a water recirculation loop around a saturation tower from which fuel gas is injected into a gas turbine combustor. The water recirculation loop is heated by recovering heat from a hot fluid by means of a heat exchanger positioned in the loop. The hot water from the loop contacts the process gas stream, i.e., fuel gas, to be moisturized in the saturation tower, which is a packed tower or other device designed to bring the hot water and the process gas stream into intimate contact. In the saturation tower, the heat added in the heat exchanger is removed through vaporization of a portion of the water stream. The vaporized water leaves the top of the saturation tower with the process gas, while the cooled water leaves the bottom of the saturator. A portion of the recirculated water is periodically removed as blowdown to control salt concentrations, and makeup water is added to replace the water lost to the moisturized gas i.e., the fuel gas stream. In the use of such a technique, the fuel gas streams that are to be moisturized need to be located near a source of heat in order to avoid the need for long and expensive water recirculation loops.
While such approaches are useful for achieving a desired moisturizing of gas streams, there remains a desire in the art for further improvements. Thus, the moderate or high pressure steam used in one approach or the long water recirculation loops frequently required in the other, represent elements of expense that desirably should be reduced to achieve the ever-increasing overall requirements for practical gas turbine applications.
It is an object of the invention, therefore, to provide an improved apparatus for such gas turbine applications.
It is another object of the invention to provide an apparatus for more efficiently operating industrial gas turbines.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof bring particularly pointed out in the appended claims.